End-stage renal disease (ESRD) affects almost 350,000 people living in the United States with an incidence that has increased by over 50% in the past decade. Total Medicare expenditures on patients with ESRD exceed $11.3 billion (U.S. Renal Data Service: 2001 Annual Data Report Atlas of End-Stage Renal Disease in the United States. Bethesda NIH, NIDDKD, 2001). The two currently treatment modalities for ESRD, dialysis and transplantation, both have significant limitations. Patients on dialysis have an extremely high mortality rate, approaching 20% per year. Patient survival is markedly improved with renal transplantation; however, the number of renal transplants is severely limited by the short supply of available organs and many patients die while awaiting transplantation of a kidney allograft.
Recently, several alternative modalities have been proposed. These include augmentation of traditional hemodialysis with a “renal assist device” consisting of xenoderived proximal tubule cells, xenotranplantation of whole developing kidney rudiments into adults, and the generation of histocompatible renal tissue using nuclear transplantation techniques.